-13- 



Table 4. - Estimated Town Costs per Pile for Planned Semi -Mechanized System 



Item Cost 



Capital Costs $ 48.00 



Wood Chips 270.00 



Labor 80.00 



Electricity 4.00 



Monitoring Piles 55.00 



Total $457.00 



Cost per wet ton of sludge 7.15 



soils, they remain there unless taken up by harvestable vegetation. Thus, 

 even if the amount of heavy metals in the sludge is modest, toxicity prob- 

 lems can develop over time. It is therefore important to determine concen- 

 trations of heavy metals in the composted sludge to determine safe applica- 

 tion rates. Heavy metal content of Durham's compost at several stages of 

 the process are provided in Table 5. For residential towns such as Durham, 

 there is little problem in this regard. However, for some industrialized 

 towns, land disposal of composted sludge may not be an acceptable alterna- 

 tive due to the presence of heavy metals. Harter ( 1975) surveyed the 

 heavy metal content of sludges in New Hampshire and found, with a few ex- 

 ceptions, that the metal content is low compared with most sludges on the 

 industrial Northeast. He also provided a means of determining the amount 

 of sludge that can be safely applied with little likelihood of toxic build- 

 up of heavy metals. 



